Ordered Mesoporous Carbons And Its Alginate Composite Adsorbents: Syntheses, Characterizations And Adsorption Performances For Methylene Blue, Chloramphenicol And Riboflavin
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Date
2014-08
Authors
Mohd Din, Azam Taufik
Journal Title
Journal ISSN
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Publisher
Universiti Sains Malaysia
Abstract
Ordered mesoporous carbons (OMC) were synthesized through nanocasting method by using lab-synthesized hexagonal mesoporous silica (HMS) as a template and polyethylene glycol 400 (PEG-400) as a carbon source. One-time variable experimental approach was deployed to study the effect of selected process parameters including carbonization temperature (873-1073 K), dwelling time (15-240 min), heating rate (1-10 K.min-1) and PEG-400 (2.5-15 g) loading on the surface area properties, yields and its ability to remove methylene blue (MB). ABA-16 sample has displayed the highest surface area of 1026 m2.g-1 with the total pore volume of 0.9976 cm3.g-1 and the average pore diameter of 3.89 nm. The presence of ordered hexagonal structure in HMS and OMCs was visualized through transmission electron microscopy (TEM). Adsorption performances of ABA-16 and MABA-16 on MB dye, chloramphenicol (CPC) antibiotic and riboflavin (RB) vitamin were investigated through batch and column operations. Batch adsorption studies was conducted at initial concentrations ranging from 50-500 mg.L-1 (MB) and 50-400 mg.L-1 (CPC and RB), temperatures (303-323 K) and pH ranging from 3-11 for MB and CPC while pH 3-7 for RB, respectively. The highest monolayer adsorption capacity, Qm was 395 and 620 mg.g-1 (MB), 210 and 223 mg.g-1 (CPC) and 464 and 222 mg.g-1 (RB) in respect to ABA-16 and MABA-16 adsorbents. At all conditions, three-parameter adsorption isotherm models produced better fittings than the two-parameter models. It was found that pseudo-second order kinetic model fitted the experimental data better than other models for MB and CPC adsorption. As for RB, the experimental data was satisfied by Elovich model at lower concentration range while pseudo-second order kinetic model could be used to describe the upper concentration range. Thermodynamics studies suggested that MB, CPC and RB adsorption on ABA-16 and MABA-16 were not in favour to increasing temperature. Alginate-carbon composite beads prepared from ABA-16 and MABA-16 were used for column operation under the following conditions; flow rates (10-30 mL.min-1), initial concentrations (50-200 mg.L-1) and bed heights (2-6 cm). Modified dose-response (MDR) model was the best model to describe dynamic behaviour of column adsorption. The decrease of 27.7, 4.0 and 15.8 % uptakes were observed on the respective composite beads upon exposure to five cycle adsorption/desorption process. As conclusions, the non-edible PEG-400 has been proven to be a viable carbon precursor for OMCs due to its safety and environmental benign properties. The produced adsorbents have displayed excellent adsorption performances for both batch and column adsorption operations.
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Keywords
Ordered Mesoporous Carbons